Many power semiconductor switches can be combined with additional low power analog and digital circuitry in one single semiconductor chip. The additional circuitry may additionally include, inter alia, driver circuits for generating driver signals to activate and deactivate the power semiconductor switches, sensor and measurement circuits for processing measured signals such as chip temperature, output current, and circuitry used for communicating with other devices such as microcontrollers or the like. The power semiconductor switches are often implemented as vertical transistors such as vertical MOSFETs or IGBTs. Vertical transistors usually have the power electrodes (e.g. drain and source electrodes in case of a MOSFET or collector and emitter electrodes in case of an IGBT) on opposing sides (top and bottom) of the semiconductor chip.
In such intelligent semiconductor switches with vertical power transistors, the substrate is usually electrically connected to one load current terminal (e.g., drain terminal, collector terminal) of the power semiconductor switch. If, for example, the power semiconductor switch is a vertical MOS transistor, the drain electrode of the MOS transistor is electrically connected to the semiconductor substrate and thus the drain potential of the transistor also defines the electric potential of the substrate. The mentioned additional analog and digital circuitry is also integrated in the semiconductor substrate, wherein the circuit components are isolated from the surrounding substrate by a pn-junction isolation. For example, the substrate may be n-doped and the mentioned additional circuitry may be implemented within a p-doped well (p-well) formed within the n-doped substrate (n-substrate). The resulting pn-junction between the n-substrate and the p-well is reverse biased during the operation of the integrated circuit and thus the pn-junction electrically isolates the circuit components in the p-well from the surrounding n-substrate.